Delay-action device employing thermionic valves



Sept. 1, 1925. 1,552,321

x N. LEA

DELAX' -AOTION DEVICE EMPLOYIN G'TH ERMIONIC VALVES Filed Jan. 11, 1922 '.5 B A T 7 i .zwwww Patented Sept. 1, 1925.

- UNITED STATES NORMAN LEA, or

, 1,552,321 PATENT OFFICE.

LONDON, ENGLAND.

DELAY-ACTION DEVICE EMPLOYING THERMIONIG VALVES.

Application filed January 11,1922. Serial No. 528,889.

nals. According to the invention, it is proposed to cause an incoming signalling current of a predetermined minimum duration to operate a local circuit by virtue of an alteration in the electrical charge of a condenser consequent upon the receipt of the incoming signal current, the operation of the local circuit at the conclusion of the predetermined time period being dependent upon a potential change as distinguished from an actual passage of current from the condenser through the local circuit.

Various further features of my invention will be seen from the following description and from the claims. It is preferred to insert the condenser, which is being charged or discharged, in the grid or control circuit of a thermionic valve arrangement. For example, the condenser so connected may be normally charged so that the grid is maintained at some definite negative potential with respect to the filament or source of electrons, but when delayed action is required, the condenser charge is allowed to leak away, with the result that after a time the negative grid potential is so reduced that an increase in anode current results suflicient to operate any desired electrical device.

It is well-known that the voltage across a resistance shunted condenser, when plotted against'time, is asymptotic to any fixed voltage which may be in series with the resistance.

Toensure that the period of delay shall be accurately determined, the rate of increase of the current which operates the electrical device at the end of the delay periodshould be large. The current flowin' through the anode circuit of the valve is a function of the potential on the grid or control electrode, and hence the rate of change of grid potential should also be as large as possible at the end of the delay riod. ,1 This requirement can befulfilled by arranging that the potential on the grid at the end of the delay period has not approached too near to its asymptotic value.

For example, using what is commonly known as a thermionic valve, the initial potential on the grid ma be 50 volts negatlve and the asymptotic v0 tage 50 volts positive with respect to the filament. In a valve of this type the anode current increases chiefly between grid otentials of say 10 and :10 volts, WlllCh is on the whole only half way between the initial and asymptotic volt-v ages, so that a rapid growth of anode current is assured at the end of the delay period.

c The invention will be described with reference to the accompanying drawing, where- 1n:

Figure 1 is a diagrammatic view showing one embodiment of the invention; and

Figure 2 is a diagram illustrating the change of the grid-voltage during the increase of the anode-current.

Referring to Figure 1, V denotes a valve of the thermionic type having a rid G, an anode A and a filament F, the last being heated by the usual battery B A condenser C is connected across the grid and filament of the valve so that the state of charge of the condenser is made to control the current passing through the anode A under the influence of a batte B with a view to operating a control devlce D and .its output contact W.

'A relay tongue T having front and back contacts M and S respectively is connected with the condenser so that. the latter is normally charged negatively on the grid side by the battery B When, however, the relay tongue is operated by an incoming signal impressed on the relay (not shown in the drawing) the tongue moves over to the contact M and the condenser 0 begins to discharge through the resistance R and if the signal is of sufii cient duration the grid will become positive enough to permit a critical current to flow through the anode circuit and hence operate the control device D. If, however, before the critical stage is reached, the relay tongue T falls back on to the contact S for even a minute period of time it suflices to charge the condenser negativel again, so that the process of discharging always starts from the same initial potential,

/namely the voltageof the battery 13,. In

this way the length of continuous signal element operating the tongue T, and requircd to bring the device D into action, is sensibly independent of the electrical history of the condenser C.

A resistance R is shown in the charging lead from the battery 13,, in order to reduce the rush of the current during the charging process disturbance in neighbouring electrical circuits.

In order to ensure that the delay action shall be well defined as regards its time of operation, we have already emphasized the importance of arranging that the grid voltage shall change rapidly during the time that the anode current is increasing. This is accomplished in the arrangement shown in Figure I by connecting the discharge resistance R, with a point on a positive battery which for convenience is shown as a point on the anode battery 13,.

The operation of the arrangement will be more clearly understood on reference to Figure 2, Where X represents the grid voltage anode-current characteristic of the valve V.

On the horizontal axis. (106, 0 represents zero grid voltage, a0 corresponds to the voltage of the negative battery 13,, and 0?) represents the voltage of that part of the battery B connected to the resistance 11,.

Before the arrival of the signal, the grid voltage is represented by the point a, but when the relay tongue T" makes contact with M, the grid voltage becomes asymptotic to the point 6 with regard to time.

The progress of the grid potential from a to b may be determined mathematically by an expotential formula involving the capacity of the condenser C, the value of the reslstance R and the voltage obtained from the battery B and the part of the battery 13,. The rate of change of grid potential is Very rapid at a and gradually falls to zero at b.

In carrying the invention into effect, the device D is preferably made to operate at or near 0 where the rate of change of grid potential is still fairly rapid, and consequently any accidental variation in the sensitiveness of the device D will have little or no influence on the period of delay. It is clear that a very high degree of accuracy of timing can be obtained by making the voltages corresponding to a0 and 06 large with respect to that corresponding to the sloping part of the valve characteristic, though in practice the batteries may be of a size commonly employed in radio te1e graphic receiving work.

As an example of an actual circuit constructed according to Figure 1 the followdata is given.

f the condenser C has a capacity of 10 microfarads, the resistance of R, is 1 megohm, the voltage of the battery T3,, is,

corresponding to the centre of the anode current characteristic is 7 seconds.

Having thus described the nature of the said invention and the best means I know of carrying the same into practical effect, I claim 1. A delay faction device comprising a three-electrode thermionic valve, an anode circuit and battery therefor, a condenser having one side thereof connected with the control electrode of said valve, a charging circuit for said condenser, means for applying through said charging circuit a negative potential to that side of the condenser connected with the cont-r01 electrode, a discharging circuit for said condenser, a resistance in said discharging circuit, a relay in the anode circuit of the valve and means energized by an incoming current operating to disconnect the condenser from the charging circuit and connect it in the discharging circuit.

2. A delay action device as claimed in claim 1, wherein the resistance in the condenser discharging circuit is connected between the control electrode and a source of positive potential.

3. A delay action relay device comprising a three-electrode thermionic valve, a condenser connected across the cathode and the control electrode of the said valve, a charging battery and circuit for said condenser, a discharging circuit for said condenser con nected across two points of the valve anode circuit, a high resistance in said discharging circuit, means actuated by the reception of an incoming current operating to disconnect the said condenser from the charging circuit and to connect it in the discharging. circuit, and a local relay included in the anode circuit of the thermionic valve.

4. A. delay action relay device, comprising a three-electrode thermionic valve, an anode circuit and battery therefor, a condenser connected across the cathode and the control electrode of the said valve, a charg ing battery and circuit for said condenser, a discharging circuit for said condenser, said circuit including a high resistance and a source of electromotive force, means actuated by the reception of an incoming current operating to disconnect the said condenser from the charging circuit and to connect it in the discharging circuit. and a local relay included in the anode circuit of the thermionic valve.

5. A delay action relay device, comprising a three-electrode thermionic valve, an anode circuit and battery therefor, a condenser connected across the cathode and the control electrode of the said valve, a chargbattery and circuit for condenser, a discharging circuit for said condenser,

. said circuit includin a high resistance and a part of the anode attery, neans actuated 5 by the reception of an mco current ep- 1, eratmg from the charging circuit and to connect to disconnect the said condenser it in the discharging circuit, and a local relayincluded in the anode circuit of the thermionic valve. 10 'In testmony whereof I have signed my name to this specification.

NORMAN LEA. 

